The present invention relates to a glow plug for an internal combustion engine, such as a diesel engine, and more particularly to a glow plug having a built-in combustion pressure sensor. The present invention also relates to a manufacturing method of a glow plug with a built-in combustion pressure sensor.
Hereinafter, the term “front” refers to a heating end side with respect to the axial direction of a glow plug, and the term “rear” refers to a side opposite the front side.
Japanese Laid-Open Patent Publication No. 2002-327919 discloses a glow plug with a built-in combustion pressure sensor. The disclosed glow plug includes a cylindrical plug housing, a sheath partly fixed in a front end portion of the housing, a heating element disposed in the sheath and a metallic center electrode disposed in the housing for power supply to the heating element. At least part of the combustion pressure sensor is disposed between a rear end portion of the housing and a rear end portion of the center electrode. The combustion pressure sensor has a piezoelectric element under compressive stress and produces an output in response to variations in the stress.